220-1101 Hardware Practice Question
A technician is building a new desktop computer. After installing the motherboard, CPU, RAM, and graphics card, the technician connects the 24-pin main power cable and all other necessary cables. When the power button is pressed, the fans spin for about one second and then stop. The motherboard's power LED does not illuminate. The technician uses a multimeter and confirms the power supply outputs 12V, 5V, and 3.3V on the appropriate pins of the 24-pin connector. Which of the following is the MOST likely cause of the issue?
⚠ Common exam trap
CompTIA often tests the misconception that a multimeter reading on the 24-pin connector proves the entire PSU is functional, when in fact the CPU power rail is separate and essential for the system to stay powered on.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The 4/8-pin CPU power connector is not connected.
The 4/8-pin CPU power connector provides dedicated 12V power to the CPU voltage regulator module (VRM). Without it, the CPU receives no power, so the system immediately shuts down after a brief fan spin (due to residual charge or a momentary power-on signal). The multimeter confirms the main 24-pin ATX connector is delivering correct voltages, ruling out a PSU failure.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
The front panel power switch header is connected to the wrong pins.
Why it's wrong here
If the power switch header is connected incorrectly, the power button would likely have no effect at all, not cause fans to spin briefly and then stop. The brief spin indicates the motherboard is receiving some power and attempting to start.
- ✓
The 4/8-pin CPU power connector is not connected.
Why this is correct
The CPU requires its own dedicated power connector (4-pin or 8-pin EPS12V) separate from the main 24-pin ATX connector. Without it, the motherboard will not power the CPU and will shut down after a brief attempt, causing the fans to spin and then stop. This matches the symptom perfectly.
- ✗
The RAM modules are not fully seated in the slots.
Why it's wrong here
Unseated or faulty RAM typically causes continuous beep codes or a failure to POST, but the system usually remains powered on (fans keep spinning). It does not cause the fans to spin briefly and then stop.
- ✗
The CMOS battery is depleted and needs replacement.
Why it's wrong here
A depleted CMOS battery only affects the motherboard's ability to retain BIOS settings, time, and date when the system is unpowered. It has no role in the main power delivery path; the system will still power on, POST, and boot with default settings even if the battery is dead. The brief fan spin followed by a shutdown instead points to a power rail or voltage regulation fault, such as the missing 4/8-pin CPU power connector, which triggers the PSU's protection circuitry, not a battery issue.
Go deeper
Related to this question
Learn chapter
Power Supply Units and Connectors
Key term
Dual In-line Memory Module
A Dual In-line Memory Module (DIMM) is a small circuit board that holds memory chips and plugs into a computer's motherboard to provide Random Access Memory (RAM).
Key term
RAM
RAM (Random-Access Memory) is volatile computer memory that temporarily stores data for quick access by the CPU.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
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